If your PC has an on board speaker or piezoelectric buzzer (and most do) they can be configured to beep on start-up using the beep utility. I find that this is particularly useful on servers such as my file server or firewall as these do not have displays. The beep lets me know when they have finished booting and are ready to use.
First you need to install the beep utility if not already installed. Open a terminal window or login on the console and enter the following commands.